Surface mounted electrical components are rapidly gaining acceptance in industry. It has been estimated that nearly one half of all electrical and electronic components may be directly surface mounted to a circuit substrate by the year 1990. Consequently, the use of lead wires with such electronic and electrical components and through holes in circuit substrates will be sharply reduced in their usage.
Presently, ceramic chip capacitors are the most commonly used surface mounted capacitors because such ceramic chip capacitors tolerate the high temperature exposure required for reflow or wave soldering manufacturing techniques, for attachment of components to circuit substrates. Metallized film capacitors and film foil capacitors have been used very little in surface mounted applications because of the high cost and greater size required to thermally protect the metallized film from such high temperature soldering techniques than attend the use of ceramic chip capacitors for similar applications.
For example, polyester film melts at about 252.degree. C. However, for an electronic part such as a capacitor, to survive wave soldering, it must withstand temperatures as high as 260.degree. C. for a period of up to ten seconds without suffering degradation in its physical or electrical properties.
One attempt to provide a leadless, surface mountable electrical component of a capacitor type has been to attach flat leads to a film capacitor section to form a capacitor assembly, which assembly is then insert molded to provide a molded package with the flat leads formed to lie adjacent the package and accessible for electrical connection. Such a package can be made capable of withstanding the thermal exposure of wave soldering or other soldering techniques sufficiently to protect its encased capacitor section. Such packages, however, are significantly more expensive than a comparable box-type capacitor where a capacitor is inserted in a plastic box and sealed in that box with such material as epoxy with leads protruding from the interior of the epoxy sealed box for electrical connection within a circuit. Thus, in view of the greater expense of the insert molded package flat lead structure described above, film capacitors (i.e. metallized film and film foil capacitors) are penalized because the economics of production costs bias industry toward ceramics and away from film capacitors for surface mountable applications.
Such economic bias is unfortunate because film capacitors, such as polyester metallized film capacitors, exhibit improved performance characteristics over many ceramic types of capacitors. Improved self healing characteristics and a higher production yield with attendant lower cost to manufacture while more consistently meeting tight specifications are but two of the improved performance characteristics of metallized film capacitors over ceramic capacitors.
It would be advantageous for circuit designers to have metallized film capacitors available for surface mounting applications, but smaller size and lower cost of manufacture than are obtainable with prior art devices and methods are economically necessary to promote sufficient usage of film capacitors in surface mounted devices to justify a manufacturer's equipping his plant for production of such capacitors.